The present invention relates to a method and apparatus for neutralizing organic alkaline wastewater and inorganic alkaline wastewater, not by using an acid as a chemical, but by converting nitrogen as an ingredient of the wastewater to nitric acid ions by aerobic microorganisms.
With higher demand for global environment maintenance in recent years and from viewpoints of environmental issues, a safe process, in which use of chemical substances is minimized, is being required.
Therefore, an environment-friendly process is similarly required even in a neutralizing method or apparatus alone. In conventional methods, however, alkaline wastewater, for example, was neutralized by adding an acid as a chemical and performing agitation.
The aforementioned method, in which the alkaline wastewater is neutralized by adding an acid as a poison, was problematic from viewpoints of safety and environment considering damages when the acid as a poison leaked and measures thereagainst or human damages or the like when the poison is touched.
It is preferable from viewpoints of both safety and environment if alkaline wastewater, for example, can be neutralized without using hydrochloric acid or the like as a poison.
Accordingly, the object of the present invention is to provide a method and apparatus for neutralizing various kinds of alkaline wastewater without using a mineral acid as a poison such as hydrochloric acid or the like.
In order to achieve the above object, there is provided a neutralizing method of neutralizing organic alkaline wastewater by producing nitric acid ions by aerobic microorganisms.
According to the above method, wastewater can be neutralized by efficiently producing nitric acid ions from organic alkaline wastewater by aerobic microorganisms.
In general, organic matters are nitrogen compounds and a large amount of nitrogen compounds are present in organic alkaline wastewater. Nitric acid ions produced from the nitrogen ingredients in the organic alkaline wastewater by aerobic microorganisms are utilized for neutralization.
Specifically, for example, wastewater can be neutralized by producing nitric acid ions from a large amount of development waste as organic alkaline wastewater discharged from a semiconductor factory or a liquid crystal factory by aerobic microorganisms.
More specifically, the development waste is alkaline wastewater with pH 12 or higher and its main ingredient is TMAH (tetramethylammonium hydroxide) containing a nitrogen compound. The chemical formula of this TMAH is (CH3)4Nxe2x80x94OH, from which NO3 ion is produced by aerobic microorganisms. Consequently, this TMAH ((CH3)4Nxe2x80x94OH) is naturally decomposed into nitric acid ions by aerobic microorganisms.
Also, there is provided a neutralizing apparatus for neutralizing organic alkaline wastewater by producing nitric acid ions by aerobic microorganisms.
According to this method, organic wastewater is mixed into inorganic alkaline wastewater so that aerobic microorganisms are propagated by using organic wastewater as a base. Since the organic matters contain nitrogen ingredients, the aerobic microorganisms microbiologically produce nitric acid ions from the organic matters. Consequently, the inorganic alkaline wastewater can be neutralized.
Also, there is provided a neutralizing method by mixing organic wastewater containing nitrogen into inorganic alkaline wastewater and producing nitric acid ions by aerobic microorganisms.
Since inorganic alkaline wastewater does not have sufficient nutrients, aerobic microorganisms cannot be propagated. The inorganic alkaline wastewater is neutralized by mixing organic wastewater (organic matters) containing nitrogen to propagate aerobic microorganisms, which produce nitric acid ions from the nitrogen. Unlike the conventional chemical neutralization method, in which hydrochloric acid or sulfuric acid as a poison is used, the neutralizing method of the present invention using microorganisms is safe since a poison is not used.
Also, there is provided a neutralizing apparatus by mixing organic wastewater containing nitrogen into inorganic alkaline wastewater and producing nitric acid ions by aerobic microorganisms.
According to this apparatus, since organic wastewater is mixed into inorganic alkaline wastewater, aerobic microorganisms are propagated by using organic wastewater as a base. Since the organic matters contain nitrogen ingredients, the aerobic microorganisms microbiologically produce nitric acid ions from the organic matters and thus the inorganic alkaline wastewater can be neutralized.
In one embodiment of the present invention, an ultrafilter membrane, a vinylidene chloride packing material, a pH meter and air supply means are included and aerobic microorganisms are utilized.
According to this apparatus, since aerobic microorganisms and an ultrafilter membrane are utilized, the aerobic microorganisms can be maintained outside the ultrafilter membrane without allowing them to flow into the inside of the ultrafilter membrane and can be cultured in a high concentration. Therefore, the organic matters can be rationally decomposed by microorganisms and nitric acid ions can be produced from nitrogen originating from the organic matters as a source. Thus, alkaline wastewater can be neutralized.
In one embodiment of the present invention, the ultrafilter membrane is a submerged membrane disposed in a water tank.
According to this constitution, since the ultrafilter membrane is provided in the water tank, a space for providing a new ultrafilter membrane is not needed.
In one embodiment of the present invention, organic wastewater containing nitrogen is an excessive domestic sludge slurry.
According to this constitution, since organic wastewater containing nitrogen is an excessive domestic sludge slurry, the excess domestic sludge slurry as unnecessary waste can be recycled, leading to effective utilization of resources at the same time.
In one embodiment of the present invention, a diffusing pipe capable of automatically adjusting a discharge amount is provided below the submerged membrane.
According to this constitution, since a diffusing pipe capable of automatically adjusting a discharge amount is provided below the submerged membrane, an air amount from the diffusing pipe can be adjusted so that both the treatment capacity of the submerged membrane and the capacity of producing nitric acid ions can be controlled. That is, the treatment capacity of the submerged membrane is determined by the air amount discharged from the diffusing pipe to some extent. The amount of nitric acid ions to be produced is determined by the air amount discharged from the diffusing pipe since the nitric acid ions are final products in the process of oxidation of nitrogen compounds.
In one embodiment of the present invention, a diffusing pipe separate from the diffusing pipe below the submerged membrane is disposed below the vinylidene chloride packing material and the amount of air discharged from this separate diffusing pipe is interlocked with the pH meter.
According to this constitution, since a diffusing pipe exclusively used for washing the submerged membrane and a diffusing pipe exclusively used for producing nitric acid ions can be separated, the air mount suitable for each purpose can be discharged from each diffusing pipe.
In one embodiment of the present invention, a dissolved oxygen meter is provided in the water tank.
According to this constitution, the limit of the amount of nitric acid ions to be produced can be obtained from a dissolved oxygen concentration measured by the dissolved oxygen meter. That is, when the dissolved oxygen concentration is high in the water tank, an increase in nitric acid ions cannot be expected even if the air amount is increased. On the contrary, when the dissolved oxygen concentration is low, the nitric acid ions can be increased, thereby reducing pH, if the air amount is increased.
In one embodiment of the present invention, a gas discharged from the separate diffusing pipe is a nitrogen gas.
Accordingly, since the gas is a nitrogen gas, nitric acid ions originating from the nitrogen gas can also be produced. The nitric acid ions can be produced more easily than by air.
Also, there is provided a neutralizing method for neutralizing alkaline wastewater by propagating aerobic microorganisms and producing nitric acid ions while a nitrogen gas and air are blown into.
According to this constitution, while the nitrogen gas (N2gas) and air (oxygen gas and nitrogen gas) are blown into, nitric acid ions are produced by using microorganisms as a catalyst and utilized for neutralization. Therefore, the amount of used nitrogen gas, which causes a high running cost, can be reduced. The amount of nitric acid ions to be produced can be easily controlled by distribution of the nitrogen gas amount and the air amount.
In one embodiment of the present invention, aerobic microorganisms are nitrate-forming bacteria or nitrite-forming bacteria.
The nitric acid ions can be efficiently produced by using nitrogen compounds as a substrate. Nitrate-forming bacteria represent a generic name of bacteria which oxidize nitrous acid ions into nitric acid ions. Nitrite-forming bacteria represents a generic name of bacteria which oxidize ammonium ions to nitrous acid ions.
In one embodiment of the present invention, a vinylidene chloride packing material and a guide are disposed below the submerged membrane, the vinylidene chloride packing material guide is disposed on both outside extension lines of the submerged membrane and a diffusing pipe is disposed therebelow.
According to this constitution, the sludge attached to a vinylidene chloride packing material and propagated is removed along the guide and raised by a gas discharged from the diffusing pipe (air or nitrogen gas) so that sludge attached to the submerged membrane can be washed. The capacity of the submerged membrane can be maintained by this wash treatment.
In one embodiment of the present invention, the vinylidene chloride packing material is composed of a plurality of ring-shaped structures extending radially.
A large amount of microorganisms can be propagated by attaching the microorganisms to the vinylidene chloride packing material composed of a plurality of ring-shaped structures extending radially.
In one embodiment of the present invention, the apparatus also serves as a biological wastewater treatment apparatus.
Not only a neutralizing function, but also a biological wastewater treatment function can be demonstrated and thus a value as an apparatus can be increased. Since this neutralizing apparatus performs neutralization by using microorganisms, naturally, the apparatus also includes a biological treatment function originally held by microorganisms. Therefore, this neutralizing apparatus can be used as a biological wastewater treatment apparatus.
In one embodiment of the present invention, the microorganism concentration within the apparatus is 10,000 ppm or higher.
The microorganisms can oxidize nitrogen in the organic matters and produce a large amount of nitric acid ions so as to neutralize alkaline wastewater. It is known that a higher microorganism concentration is preferable for this neutralizing apparatus to perform its functions to some extent. The MLSS concentration is preferably 10,000 ppm or higher, most preferably, about 20000-30000 ppm.
Sludge has an action of neutralizing wastewater. When the sludge concentration (MLSS) is high, the neutralization action is enhanced as shown below. Here, an experiment was performed under a condition that only 100 cc of wastewater with pH 11 was added to 1000 cc of biological sludge (that is, the total liquid amount is 1100 cc).
In one embodiment of the present invention, the treatment capacity of the submerged membrane is controlled by the amount of air discharged from the diffusing pipe disposed below the vinylidene chloride packing material.
According to the above constitution, sludge attached to the vinylidene chloride packing material can be removed by air discharged from the diffusing pipe disposed below the vinylidene chloride packing material. Since the submerged membrane surface is washed with wastewater containing air and sludge, the submerged membrane surface can be reliably washed.
When the submerged membrane is used for a certain time period, sludge or the like is attached to its surface and thereby its treatment capacity is degraded. Therefore, conventionally, the submerged membrane surface was washed by air aeration to recover a predetermined treatment capacity.
One important point in the present invention is to substantially increase the microorganism concentration in the water tank. However, there is a problem caused by this increase in the microorganism concentration. That is, the submerged membrane is blocked by the sludge as described later. Therefore, in the present invention, the vinylidene chloride packing material is arranged below the submerged membrane so that sludge is removed from the vinylidene chloride packing material by aeration. The above-described problem is solved by thus xe2x80x9cwashing the submerged membrane by sludgexe2x80x9d regularly.
Conventionally, it is known that weakly alkaline wastewater can be neutralized to some extent when nitric acid ions are produced. However, one important point in the present invention is that a large amount of nitric acid ions are produced by substantially increasing the microorganism concentration to neutralize strongly alkaline wastewater as well.